The invention relates to an apparatus and a method for processing value documents, in particular for controlling the feed of a value document stack.
For EP0865398 B1 there is known a singler for value documents, by which value documents are singly withdrawn from a value document stack. Therein, a value document stack resting on a movable pressure plate is supplied to the singler by lifting the pressure plate. The singler has an advancing device, a singling roller and a retaining device. For singling the sheet material, the pressure plate is moved in the direction of the singler, until the value document stack is urged against the advancing device with slight pressure. Thereafter, the respective uppermost value document of the stack is moved by means of the advancing device in the direction of the singling roller which then singles the uppermost value document. As the number of value documents in the value document stack decreases with progressing singling, the pressure plate is continuously fed upward, in order to further lift the value document stack so that respectively the uppermost value document can be grasped by the advancing device of the singler.
For suitably feeding the value document stack, the density of the value documents in the stack is continuously determined during singling. The stack can thus be urged against the advancing device of the singler with a suitable pressure during the whole singling. For determining the density of the value document stack there is employed e.g. a camera which is directed to the side of the value document stack, in order to capture an image of the value document edges. By means of image processing the value document edges are recognized and therefrom the density of the value document stack is ascertained, i.e. the number of value documents in a certain section of the value document stack. In dependence on the ascertained number of value documents the distance between the pressure plate and the singler is controlled.
With the hitherto known image processing methods a recognition of the value document edges is not always possible, however. Therefore, image processing methods were proposed, which allow an improved edge recognition, e.g. in WO2011161642 A1. Furthermore, in EP1576552 B1 it was proposed to magnify the recorded image of the value document edges in the direction along the stack and to increase the number of pixels along the stack direction, so as to achieve a more accurate edge recognition. In the case of heavily used value documents for which the edge recognition does not work in the EP 1576552 B1 it was proposed to mechanically cut the value document stack, so that the used value documents obtain a new clean cut edge, and to subsequently carry out the edge recognition on the basis of the obtained clean cut edges.